Process of catalytic cracking with a siliceous catalyst containing lithium hydroxide



United States Patent Sun Oil Company, Philadelphia, Pa.,- a corporation of New Jersey No Drawing. Application October 20, 1955 Serial No. 541,820

This invention relates to a process for cracking hydrocarbons. More particularly the invention relates to a process for the catalytic cracking of hydrocarbons to obtain a high yield of gasoline and only a minor quantity of coke.

Processes for cracking hydrocarbons using a variety of catalysts and reaction conditions have heretofore been described. Such processes generally seek to obtain a high yield of gasoline while producing only minor quantities of coke since, as is well known, coke formation'causes rapid catalyst deactivation. However, heretofore described processes generally operate so that when a satisfactory gasoline yield is obtained, a high yieldof coke is also obtained. This necessitates frequent catalyst'regenerati'on or replacement. v I

An object of the present .inventionis .toprovide a process for converting hydrocarbons of relatively high boiling petroleum fractions to hydrocarbons boiling in the gasoline range without concomitant production of appreciable amounts of coke. Another object is to provide a process for cracking hydrocarbons wherein long operation with a good yield of gasoline is obtained without catalyst deactivation. A further object is to provide a process for converting relatively high boiling petroleum fractions to gasoline in goodyield without substantial catalyst deactivation, wherein the higher boiling fractions have an increased content of normal paraflins which are readily converted to desirable products in subsequent operations. Other objects and their achievement in accordance with the invention will be apparent hereinafter.

It has now been found that by contacting a relatively high boiling petroleum fraction with a siliceous cracking catalyst which contains a small quantity of lithium hydroxide, as hereinafter described, the hydrocarbons of the high boiling petroleum fraction are converted in good yield to hydrocarbons boiling within the gasoline range with concomitant formation of only a relatively small quantity of coke.

In accordance with the process of the invention, a relatively high boiling petroleum fraction having a substantial content of straight chain hydrocarbons, or substantially straight chain hydrocarbons, is contacted under cracking conditions with a siliceous cracking catalyst, such as a silica-alumina cracking catalyst, which contains a small quantity of lithium hydroxide. The hydrocarbon effluent from the process is distilled to separate a gasoline fraction and at leastone fraction boiling above the gasoline range. The higher boiling fraction or fractions contain a proportion of straight chain hydrocarbons, by which term is included substantially straight chain hydrocarbons, i.e. hydrocarbons which have only a slightly branched chain, substantially greater than the proportion thereof in the initial feed stock. Such fractions are especially suitable ctor use in thermal cracking, in processes which combine dehydrogenation and cyclization to produce aromatic hydrocarbons, or in isomerization processes to produce materials which are valuable without further 2 processing or which can advantageously be recycled in the present process.

The relatively high boiling petroleum fractions Which can be used in the process of the invention are the petroleum cracking stocks boiling above the gasoline range, say above about 400 F. Such fractions normally contain straight chain p'arafiins, and the process of the inventiori is especially valuable with such fractions containing substantial quantities thereof, say from about 10-60% by volume straight chain parafiins'. The remaining hydrocarbons of the fractiongenerally consist of isoparaffins, naphthenes and aromatics, including alkyl-substituted naphthenes and aromatics. Straight run petroleum fract'ion's generally are suitable, but other fractions, such as cracked fractions including olefins, can be used if desired.

The catalyst used in the process ofthe invention is a siliceous'cracking catalyst which contains a small amount of lithium hydroxide. By siliceous cracking catalyst, and terms of similar import as used herein, is meant a synthetic or natural siliceous composition known to be efifective for the cracking of hydrocarbons. Synthetic silica-alumina cracking catalysts form the preferred catalyst o'fthe process of the invention, and the process is hereinafter largely described in terms thereof. However, other siliceous cracking catalysts give good results, such as silica-magnesia, silica-zirconia, silica-alumina-zirconia, and acid activated clays, such as acid activated montmorillonite.

The siliceous cracking catalyst used in the process of the inventionnmay be prepared by means heretofore known. For example, the silica-alumina portion of the catalytic composition can be prepared by impregnating silica with aluminum salts, by directly combining precipitated hydrated alumina andsilica, or by joint precipitation of alumina and silica from aqueous solutions of their salts. It is preferred'to prepare the cracking component before deposition" thereon of lithium hydroxide, i,e., the cracking catalyst should be dried and. calcined prior to the deposition of lithium hydroxide. The lithium hydroxide is advantageously deposited on the cracking catalyst by means of an aqueous solution. For example, an aqueous solution of lithium hydroxide containing a quantity of lithium hydroxide sufficient to impart the desired quantity thereof to the final catalyst is contacted with the silicaalumina composition. Excess solution is drained, if nesessary, and the resulting composition dried and calcined. The quantity of litlnum hydroxide must be within the range of from 0.2 to 2 milli-equivalents (meq) per gram of catalyst. If smaller amounts are used, substantial coke formation is observed, whereas if larger quantities above the stated maximum range are used, the cracking activity of the composition is decreased so that an operable yield of gasoline is not obtained.

A significant advantage of the process is the high yield of gasoline obtained compared to the yield of coke formed, i.e. the selectivity of the process for producing gasoline is excellent, whereas the selectivity for producing coke is poor. The ratio of gasoline produced to coke formed is a convenient measure of selectivity, and is determined by dividing the volume percent gasoline formed by the weight percent coke formed. In general, processes heretofore described give a gasoline to coke ratio of from about 8 to 20. In the process of the present invention a gasoline to coke ratio of at least 25, say from 25 to 37, is achieved.

In carrying out the process of the invention, cracking conditions are used. By cracking conditions is meant the conditions known to the art to be useful for the catalytic cracking of hydrocarbons. To illustrate operable conditions, temperatures of from about 750 F. to 1100 square inch gauge (p.s.i.g.), and space rates of from 0.5-5 volumes of hydrocarbons per volume of catalyst per hour (v./v./hr.), give good results. The process of the invention can be operated using fixed bed or continuous bed techniques, or fluidized operation may be used.

The following example illustrates the process of the invention:

A petroleum fraction consisting of about volume percent straight chain paraffins and about 30 volume percent naphthenes, the remainder being isoparaflins and aromatics, and which boils in the range of from about 407 F. to about 750 F., as contacted with a synthetic silica-alumina cracking catalyst containing about 0.6 meq.

of lithium hydroxide per gram of catalyst, cracking conditions of about 900 F., atmospheric pressure, and a eifluent from the catalyst contacting is distilled to obtain a yield of gasoline of about 40% by volume. The amount of coke formed is minor, being about 1.2% by weight. The gasoline to coke ratio (yield of gasoline in volume percent divided by yield of coke in weight percent) is therefore 33.3. The fraction remaining after the removal of gasoline has an increased proportion, about 35% by volume, of normal paraffins.

Repeating the process using the same silica-alumina composition without lithium hydroxide, and using substantially the same cracking conditions, a yield of about 42 percent by volume gasoline with a gasoline to coke ratio of about 12 is obtained.

The invention claimed is:

1. Process for the preparation of gasoline from a petroleum cracking stock which comprises: contacting, under cracking conditions, said relatively high boiling cracking stock with a siliceous cracking catalyst which contains from about 0.2 to 2 milli-equivalents of lithium hydroxide per gram of catalyst.

2. Process for the preparation of gasoline from a relatively high boiling petroleum cracking stock containing at least 10% by volume straight chain hydrocarbons which comprises: contacting, under cracking conditions, said relatively high boiling cracking stock with a siliceous cracking catalyst which contains from about 0.2 to 2 milli equivalents of lithium hydroxide per gram of catalyst, and separating from the hydrocarbon effluent a gasoline fraction and a higher boiling. fraction having an increased proportion of straight chain parafiins.

3. Process for the preparation of gasoline from a relatively high boiling petroleum cracking stock containing from about 10% to by volume straight chain paraffins which comprises: contacting said relatively high boiling petroleum cracking stock with a catalyst consisting essentially of a siliceous cracking catalyst which contains from about 0.2 to 2 milli-equivalents of lithium hydroxide per gram of catalyst under cracking conditions to produce gasoline and coke in a ratio of gasoline to coke of at least 25.

4. Process for the preparation of gasoline from. a relatively high boiling petroleum cracking stock containing from about 10% to 60% by volume straight chain paraffins which comprises, contacting said relatively high boiling petroleum cracking stock with a catalyst consisting essentially of a siliceous cracking catalyst which contains from about 0.2 to 2 milli-equivalents of lithium hydrox ide per gram of catalyst under cracking conditions to pro duce gasoline and coke in a ratio of gasoline to coke of at least 25, separating gasoline from the reaction product and separating a relatively high boiling fraction having an increased content of straight chain hydrocarbons.

5. Process according to claim 4 wherein said siliceous cracking catalyst is a silica-alumina cracking catalyst.

6. Process according to claim 4 wherein said siliceous cracking catalyst is a silica-magnesia cracking catalyst.

7. Process according to claim 4 wherein said siliceous cracking catalyst is a silica-zirconia cracking catalyst.

8. Process according to claim 4 wherein said siliceous cracking catalyst is a silica-alumina-zirconia cracking catalyst.

9. Process according to claim 4 wherein said siliceous cracking catalyst is an acid activated natural clay cracking catalyst.

References Cited in the file of this patent UNITED STATES PATENTS 2,474,440 Smith et a1. June 28, 1949 

1. PROCESS FOR THE PREPARATION OF GASOLINE FROM A PETROLEUM CRACKING STOCK WHICH COMPRISES: CONTACTING, UNDER CRACKING CONDITIONS, SAID RELATIVELY HIGH BOILING CRACKING STOCK WITH A SILICEOUS CRACKING CATALYST WHICH CONTAINS FROM ABOUT 0.2 TO 2 MILL-EQUIVALENTS OF LITHIUM HYDROXIDE PER GRAM OF CATALYST. 